1. Field of the Invention
The present invention relates generally to tissue cutting instruments having an elongate inner member rotatably disposed in an elongate outer tubular member to cut anatomical tissue and, more particularly, to angled tissue cutting instruments and methods of fabricating angled tissue cutting instruments having an elongate flexible inner tubular member rotatably disposed in an elongate angled outer tubular member.
2. Discussion of the Related Art
Surgical cutting instruments in which an elongate inner member is rotated within an elongate outer tubular member have become well accepted in surgical procedures where access to a cutting site in a patient's body is gained via a narrow or small size natural or surgically created anatomical opening or passage establishing communication with the cutting site from externally of the patient's body. Typically, the outer tubular member includes a distal end with an opening defining a cutting port or window, and the inner member includes a distal end carrying a cutting configuration exposed by or from the cutting port for engaging anatomical tissue at the cutting site. Proximal ends of the inner and outer members ordinarily include hubs which attach to a powered handpiece disposed externally of the patient's body and having a motor for rotating the inner member relative to and within the outer member. The cutting configuration of the inner member can have various configurations depending upon the surgical procedure to be performed, the type of tissue to be cut and/or the desired cutting action. The opening in the distal end of the outer member may be suitably configured to cooperate with the particular cutting configuration of the inner member to cut anatomical tissue. Often the inner member is tubular and has an aspiration port at its distal end communicating with the lumen of the inner tube so that material, including loose tissue resulting from a cutting procedure, can be aspirated from the cutting site through the aspiration port and lumen of the inner member. Many tissue cutting instruments are designed to allow irrigating fluid to flow along the instruments for discharge at the cutting site, and some tissue cutting instruments are designed for flow of irrigating fluid between the outer and inner members. It is advantageous in tissue cutting instruments for the direction of rotation of the inner member to be reversible during operation for operation of the instruments in both forward and reverse rotational directions. An example of a rotary tissue cutting instrument of the aforementioned type is described in U.S. Pat. No. 4,203,444 to Bonnell et al for use in performing arthroscopic knee surgery.
Many tissue cutting instruments are straight, with longitudinally or axially straight inner and outer members as represented by the Bonnell et al patent. In straight tissue cutting instruments, it is typical for the outer tubular member to comprise an outer tube and for the inner tubular member to comprise an inner tube having an outer diameter for being accommodated in the inner diameter of the outer tube while allowing the inner tube to rotate within the outer tube. Typically, there is a small annular gap or clearance between the outer diameter of the inner tube and the inner diameter of the outer tube, and irrigating fluid may flow along the irrigation channel defined by this gap or clearance for discharge through the cutting port. The lumen of the inner tube defines the aspiration passage in communication with the aspiration port at the distal end of the inner tube and through which material is aspirated when suction is produced in the lumen of the inner tube. Since an elongate body of the straight inner tube is normally of unbroken solid wall construction, there are no openings through the wall of the body of the inner tube through which suction in the aspiration passage may be lost and/or through which irrigating fluid may be drawn into the aspiration passage.
In many surgical procedures, it is advantageous for the tissue cutting instruments to be non-straight or angled to access cutting sites which are not accessible or are more difficult to access with straight tissue cutting instruments. Angled tissue cutting instruments normally comprise an elongate angled outer tubular member and an elongate flexible inner tubular member which conforms to the angled configuration of the outer member while being rotatable therein. The angled configuration of the outer member can be formed by various angles, bends or curves, as limited by the ability of the flexible inner tubular member to bend. As with straight tissue cutting instruments, irrigating fluid may flow through an irrigation channel between the angled outer tubular member and the flexible inner tubular member, and aspiration may be conducted through an aspiration passage of the flexible inner tubular member.
The flexible inner tubular members of many angled tissue cutting instruments utilize spirally or helically wound coils or springs to transmit torque to rotate the cutting configuration when the inner members are rotated within the outer members. Flexible inner members that employ a single spirally or helically wound coil to impart flexibility while transmitting torque are represented by U.S. Pat. No. 4,466,429 to Loscher et al and U.S. Pat. No. 4,445,509 to Auth. A single coil tends to unwind when rotated in a direction opposite its winding so that torque can only be transmitted efficiently in one rotational direction. Accordingly, angled tissue cutting instruments utilizing this type of flexible inner member cannot be operated in both forward and reverse rotational directions.
Flexible inner tubular members having a plurality of coaxial spirally or helically wound coils disposed one on top of the other and wound in alternating opposite directions relative to one another have been used in angled tissue cutting instruments to transmit torque in both rotational directions. U.S. Pat. No. 4,646,738 to Trott describes an angled tissue cutting instrument in which the flexible inner tubular member comprises separate distal and proximal end portions and a composite spiral interposed between the distal and proximal end portions to allow the inner tubular member to bend. The composite spiral is similar to the flexible shaft disclosed in U.S. Pat. No. 177,490 to Fones et al and is made up of an inner spiral, a middle spiral and an outer spiral arranged one on top of the other with their windings alternating in direction. The distal and proximal end portions include reduced diameter neck portions which are telescopically received within opposite ends of the inner spiral to facilitate welding of the distal and proximal end portions to opposite ends of the composite spiral. Each spiral adds material and labor costs to the flexible inner tubular member and, therefore, to the angled tissue cutting instrument. Another disadvantage of the flexible inner tubular member used in the Trott instrument is that the neck portions tend to stiffen the composite spiral in the vicinity of the cutting tip thereby preventing the inner member from bending adjacent the cutting tip. In addition, it is possible for the separate components to become detached from one another during use such that torque can no longer be effectively transmitted to the cutting configuration. Angled tissue cutting instruments in which the flexible inner tubular member is like that disclosed in the Trott patent are described in U.S. Pat. No. 5,286,253 to Fucci and U.S. Pat. No. 5,529,580 to Kusunoki et al.
U.S. Pat. No. 5,314,438 to Shturman and U.S. Pat. No. 6,217,595 to Shturman et al relate to a flexible drive shaft comprising inner and outer oppositely wound helical wire layers along the entire length of the drive shaft. The drive shaft of the Shturman patent is referred to in the Shturman et al patent as being difficult and time-consuming to manufacture. The drive shaft of the Shturman et al patent has its outer helical layer made up of a single wire and its inner helical layer made up of a plurality of wires, which must all be wound around a forming mandrel so that the drive shaft requires many parts and is still difficult and time-consuming to manufacture. Flexible shafts or tubular members comprising two layers of helical windings or coils have many of the same disadvantages as flexible tubular members that have three helical windings or coils.
Another disadvantage associated with the use of helical coils or springs to transmit torque while imparting flexibility is that spaces or gaps between the coils may be presented along the body of the flexible inner tubular member which allow suction in the lumen or aspiration passage of the inner tubular member to be dissipated such that less suction is applied at the aspiration port for reduced aspiration efficiency. A weakened suction force or vacuum in the aspiration passage and/or at the aspiration port may lead to clogging or jamming of the tissue cutting instrument due to tissue build-up. Clogging or jamming of tissue cutting instruments due to tissue build-up undesirably leads to the need for frequent cleaning or substitution of the instruments during use, which is time consuming and increases the duration of the surgical procedure to the detriment of the patient and the surgeon. Loss of irrigation efficiency is another problem where spaces are presented between the coils, since irrigating fluid flowing between the outer and inner members may be drawn through the spaces into the aspiration passage. An additional drawback of helical coils or springs is the tendency of the coils or springs to require tightening or preloading. Furthermore, coils or springs have a tendency under certain loading conditions to relax or unwind, and thus expand, thereby increasing the possibility of the inner member binding within the outer member. Relaxation of the coils or springs also makes it more likely that sizable spaces or gaps will be presented between the coils, especially on bending, through which suction in the lumen of the inner member may be lost and/or through which irrigating fluid flowing between the inner and outer members may be drawn into the inner member lumen.
U.S. Pat. No. 5,922,003 to Anctil et al relates to an angled tissue cutting instrument and to a method of fabricating an angled tissue cutting instrument in which the flexible inner tubular member has a flexible region interposed between a drive shaft and a cutting tip. The flexible region includes a flexible polymeric tube having ends that receive necks of the drive shaft and cutting tip, respectively. A collar of heat shrink tubing is disposed over each end of the tube. When heat is applied, the collars shrink and the polymeric material is caused to flow into slots in the necks to form a mechanical joint. The heat shrunk tubing may be removed after the polymeric material has cured. Counter wound wires embedded in the polymeric material assist in transmitting torque in forward and reverse rotational directions.
Another approach to flexible inner tubular members of angled tissue cutting instruments has involved forming relief apertures or slots through the walls of solid inner tubes to impart flexibility to the inner tubes as represented by U.S. Pat. No. 5,152,744 and U.S. Pat. No. 5,322,505 to Krause et al. In the angled tissue cutting instruments described in the aforementioned Krause et al patents, the inner tubes have discrete, unconnected apertures or slots formed therein such that torque transmission is limited. Also, the slots present spaces through which fluid can flow to and from the lumen of the inner tube.
U.S. Pat. No. 5,807,241 to Heimberger discloses a flexible tube particularly useful as a shank for a flexible endoscope. The flexible tube is formed by cutting a gap in a closed path in a longitudinally straight solid tube to form interlocking but completely materially or physically separated tube sections that allow the tube to bend axially. The flexible tube may not be well suited for use as a rotatable inner tubular member of a surgical cutting instrument since its torque capabilities may be limited to relatively low single direction and bidirectional rotational speeds. Additionally, it is possible for the individual tube sections to disconnect or become detached when the tube is bent. Spaces are presented between the individual tube sections allowing the exchange of fluid between the outside and the inside of the tube.
Angled tissue cutting instruments having inner tubes with continuous helical cuts therein to impart flexibility are illustrated by U.S. Pat. No. 6,053,922 to Krause et al, U.S. Pat. No. 6,312,438 B1 to Adams and U.S. Pat. No. 6,533,749 B1 to Mitusina et al. In the angled tissue cutting instruments disclosed by Krause et al '922, no additional layer of material is secured over the helically cut inner tube. Accordingly, the instrument may be suitable for transmitting torque in one direction only and may be of limited torsional strength, as well as the helical cut presenting a space through the wall of the inner tube through which fluid may flow. The angled tissue cutting instruments described in the Adams and Mitusina et al patents have flexible inner tubular members including flexible regions formed by a helical cut in an inner tube and two spiral wrap layers disposed over the helical cut in the inner tube one on top of the other in alternating directions. The instruments disclosed in the Adams and Mitusina et al patents overcome the primary disadvantages of wound helical coils or springs and can effectively transmit torque in both rotational directions at relatively high rotational speeds with minimal wind-up and with the structurally interconnected inner tube eliminating the problems of disconnection or detachment of the inner tube. The use of multiple spiral wrap layers over the helical cut reduces but does not eliminate the possibility of suction being lost from the lumen of the inner tube and/or irrigating fluid entering into the lumen of the inner tube since the helical cut and spiral wraps still present spaces for fluid flow between the outside and the inside of the tubular member. The use of a helically cut inner tube achieves a high degree of bendability and allows flexibility to be imparted to the inner tube adjacent the cutting configuration. However, each spiral wrap layer adds material and labor costs to the flexible inner tubular member and, therefore, to the angled tissue cutting instrument.
It would be desirable to provide an alternative construction for the flexible inner tubular members of angled tissue cutting instruments wherein the flexible inner tubular members retain the benefits of utilizing a helically cut inner tube and allowing torque transmission in forward and reverse rotational directions, while replicating a solid wall inner tubular member construction for increased aspiration and irrigation efficiencies and reduced risk of clogging, reducing wind-up, providing increased structural strength, and reducing the labor and materials needed to fabricate the flexible inner tubular members of various diametric sizes of angled tissue cutting instruments having angled outer members with angles of various magnitudes, radii of curvature and directions.